Typically, a pneumatically actuated fastener-driving tool, such as a pneumatically actuated nail-driving tool or a pneumatically actuated staple-driving tool, comprises a cylinder, a piston movably axially within the cylinder, and a driving element movable conjointly with the piston. The driving element, which may also be called a driver blade, moves through a central aperture of a end wall of the cylinder in a driving stroke of the piston and in a return stroke of the piston. The piston is arranged to be forcibly moved toward the end wall having the central aperture in a driving stroke and to be oppositely moved in a return stroke. In a driving stroke of the piston, the driving element moves along a drive track and drives a fastener, such as a nail or staple fed into the drive track from a magazine containing a strip or coil of collated fasteners, into a workpiece. Such a tool is exemplified in Bojan et al. U.S. Pat. No. 3,552,274 and in Howard et al. U.S. Pat. No. 3,815,475.
Typically, such a tool also comprises a resilient or elastomeric bumper, which arrests axial movement of the piston in a driving stroke. As exemplified in Wandel et al. U.S. Pat. No. 3,496,840 and in British Patent Specification No. 1,496,295 to Signode Corporation, it is known for such a bumper to have chamfers, axial flutes along an outer surface, or axial bores, which affect its response to heavy impacts, and which affect air circulation along its outer surfaces.
Ideally, such a bumper should exhibit high tensile strength, high elongation to breakage, high tear strength, high fatigue strength, low hysteresis, and low changes in modulus over a wide range of operating temperatures, which can range from about -20.degree. F. to about 200.degree. F. It is difficult to optimize such properties in such a bumper, which typically is made of a resilient or elastomeric material, such as a natural or synthetic rubber.
For such bumpers, cast polyurethanes have superior properties, as compared to other natural or synthetic materials, except that strength values of cast polyurethanes drop rapidly when their temperatures remain elevated for prolonged periods, particularly but not exclusively as a consequence of internal material friction due to repeated impacts over short intervals of time. Strength values of other materials used for such bumpers tend to be similarly affected by elevated temperatures.
Accordingly, there has been a need heretofore for a better way to cool such a bumper, particularly but not exclusively such a bumper made of a cast polyurethane.